IB DP Environmental Systems and Societies – Biodiversity, human impacts and conservation Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

This practice set is for Topic 3, Biodiversity and conservation, of IB Diploma Programme Environmental Systems and Societies. It is aligned to the IB Diploma Programme Subject Brief, Environmental systems and societies, and covers syllabus sections 3.1–3.3: biodiversity and evolution, human impact on biodiversity, and conservation and regeneration. All questions suit both SL and HL; HL students study some topics in extra depth. It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions.

The brief gives Topic 3 Biodiversity and conservation 13 teaching hours at SL and 26 at HL. It does not list the subtopics or learning outcomes for this topic, so the numbered subtopics and outcomes on this page follow the syllabus numbering used in the printable ESS checklist, not the brief itself.

Learn the content first with the biodiversity and conservation study guide and the revision notes. The IB DP ESS course hub and the printable ESS syllabus checklist show the whole course. For food-web questions, use the Topic 2 Ecology practice set. All data below are invented.

Questions

1. Define genetic diversity and habitat diversity. [2]

2. Distinguish between species richness and species evenness. [2]

3. Outline how geographical isolation can lead to the formation of a new species. [4]

4. (Data response) Fish were counted along one 50 m transect at each of two reef sites, using the same method on the same day.

Species	Site 1 (protected)	Site 2 (fished)
A	14	30
B	11	12
C	9	3
D	7	2
E	5	1
F	2	0
Total	48	48

Simpson’s reciprocal index: D = N(N − 1) / Σn(n − 1)

(a) Calculate D for Site 1. [2] (b) Show that D for Site 2 is 2.23 to 3 significant figures. [2] (c) Suggest two reasons for the difference in D between the sites. [2]

5. Outline how movements of tectonic plates can affect biodiversity. [3]

6. Explain why a species with a specialised niche and a low reproductive rate is more vulnerable to extinction than a generalist species that breeds quickly. [4]

7. (Data response) A survey counted adults of a fictional frog species, Species F, in its only wetland.

Year	2010	2014	2018	2022
Adults counted	3200	2250	1400	880

(a) Calculate the percentage decline from 2010 to 2022. [2] (b) Calculate the mean rate of decline from 2010 to 2022. [2] (c) Using percentage changes, compare the decline in 2010–2014 with the decline in 2018–2022. [2] (d) State two further pieces of information, other than population trend, that the IUCN Red List uses to assess threat. [2]

8. (Data response) Two proposed reserves each cover 36 km². Reserve X is a 6 km × 6 km square. Reserve Y is a 12 km × 3 km rectangle. Edge effects reach 1 km inside every boundary.

(a) Calculate the core area and the percentage of the total area that is core for each reserve. [4] (b) Calculate the perimeter of each reserve. [1] (c) Explain, with reference to edge effects, why Reserve X is likely to support more species that need interior habitat. [2] (d) Outline one argument for protecting several smaller reserves instead of one large one. [1]

9. Distinguish between a keystone species and a flagship species, giving an example of each. [3]

10. Evaluate captive breeding and reintroduction as a way of conserving an endangered species. [6]

11. (Data response) Bird species were recorded in five forest fragments of different sizes.

Fragment area / ha	1	5	20	80	320
Bird species	8	14	21	30	41

(a) Describe the relationship between fragment area and the number of bird species. [2] (b) Calculate the percentage increase in species from the 20 ha fragment to the 320 ha fragment. [2] (c) Explain two reasons why larger fragments hold more species. [2]

12. To what extent can rewilding reverse the loss of biodiversity caused by habitat fragmentation? [9]

Answers

1. Genetic diversity: the range of different genes or alleles within a species or population [1]. Habitat diversity: the range of different habitats or ecosystems in an area [1]. [2] Examiner insight: A definition must state its scope (“within a species”, “in an area”); “variety of genes” alone often loses the mark.

2. Richness is the number of different species present [1]; evenness is how similar the population sizes (relative abundances) of those species are [1]. [2] Examiner insight: “Distinguish” needs both sides stated; defining only richness and writing “evenness is the opposite” earns one mark at most.

3. A physical barrier (e.g. sea or mountains) splits a population [1]. Gene flow between them stops [1]. Each population meets different selection pressures, so different alleles are favoured [1]. Over many generations they can no longer interbreed to produce fertile offspring [1]. [4] Examiner insight: “Gene flow stops” is a separate marking point that many answers skip.

4. (a) N(N − 1) = 48 × 47 = 2256 and Σn(n − 1) = 182 + 110 + 72 + 42 + 20 + 2 = 428 [1]; D = 2256 / 428 = 5.27 [1] (b) Σn(n − 1) = 870 + 132 + 6 + 2 + 0 = 1010 [1]; D = 2256 / 1010 = 2.2337… = 2.23 (3 s.f.) [1] (c) Site 2 has lower richness (5 species, not 6) [1]; Site 2 is much less even, dominated by species A, perhaps because fishing removes the larger target species and leaves one tolerant species [1]. Examiner insight: In a “show that” question the final value is given, so marks come only from visible working; writing 2256/1010 without listing the n(n − 1) terms risks losing the method mark.

5. Separation of land masses isolates populations, leading to speciation [1]. Colliding plates build mountains, creating new habitats and barriers [1]. Land bridges let species spread into new areas and compete with existing species [1]. [3] Examiner insight: Each point needs the effect on biodiversity, not just the geological event.

6. A specialist depends on a narrow range of food or habitat [1], so it cannot switch if that resource is lost [1]. A low reproductive rate means the population recovers slowly after a decline [1] and produces fewer offspring, so there is less variation for selection to act on when conditions change [1]. [4] Examiner insight: “Explain” needs each feature linked to vulnerability with a “so…”; a bare list earns about half the marks.

7. (a) (3200 − 880) / 3200 × 100 [1] = 72.5% [1] (b) 2320 / 12 [1] = 193 adults per year (3 s.f.) [1] (c) 2010–2014: (3200 − 2250) / 3200 × 100 = 29.7%; 2018–2022: (1400 − 880) / 1400 × 100 = 37.1% [1]; so the rate of decline is increasing (accelerating) [1]. (d) Any two: geographical range size; degree of fragmentation; number of mature individuals; probability of extinction in the wild [1] [1]. Examiner insight: A rate needs units; “193” alone may lose the accuracy mark, and using 880 rather than 3200 as the base in (a) loses both marks.

8. (a) X: core side 6 − 2 = 4 km, core area 16 km², 16/36 = 44.4% [1] [1]. Y: core 10 km × 1 km = 10 km², 10/36 = 27.8% [1] [1]. (b) X: 24 km; Y: 30 km (both needed) [1] (c) Y has a longer boundary for the same area, so a larger share of it is exposed to light, wind, drying, predators and invasive species [1]; X has a larger core, so interior species have more suitable habitat and can maintain larger populations [1]. (d) Several reserves spread risk, so one fire or disease outbreak is unlikely to affect all of them (or: they can cover a wider range of habitat types) [1]. Examiner insight: Examiners normally allow error carried forward, so a wrong core area in (a) can still earn full marks in (c) if the reasoning is correct; the edge depth must come off both sides.

9. A keystone species has an effect on its ecosystem much larger than its abundance suggests, e.g. sea otters controlling sea urchins in kelp forests [1]. A flagship species is a charismatic species used to attract public support and funding, e.g. the giant panda [1]. Keystone status is about ecological role, while flagship status is about human appeal [1]. [3] Examiner insight: The third mark is for an explicit contrast; two separate definitions often stop at two marks.

10. Indicative points, one mark each (other valid points, such as raising public awareness or high cost, can also earn credit):

• Strength: keeps a species alive when wild numbers are too small to survive [1].
• Strength: breeding programmes can use records to choose pairs and reduce inbreeding [1].
• Limitation: captive populations are small, so genetic diversity is lost [1].
• Limitation: animals may lose natural behaviours such as hunting or predator avoidance, so reintroductions can fail [1].
• Limitation: if the original threat (habitat loss, hunting) is not removed, the reintroduced population declines again [1].
• Judgement: most effective as a short-term rescue combined with habitat protection [1]. [6] Examiner insight: “Evaluate” requires strengths, limitations and a conclusion; an answer with only strengths, however detailed, cannot reach full marks.

11. (a) The number of species increases with fragment area (8 species at 1 ha, 41 at 320 ha) [1]; the gain per hectare falls at larger areas: 1 to 5 ha adds 6 species for 4 ha, but 80 to 320 ha adds only 11 species for 240 ha [1]. (b) (41 − 21) / 21 × 100 [1] = 95.2% [1] (c) Larger fragments contain more habitat types, so more niches [1]; they support larger populations that are less likely to die out, and have a larger core with fewer edge effects [1]. Examiner insight: “Describe” answers gain credit for quoting data from the table with units (ha); a trend statement without figures is often limited to one mark.

12. Indicative points, one mark each. In the real exam, extended answers are marked holistically against the IB’s own assessment criteria, not point by point, so treat these points as a guide:

• Fragmentation reduces biodiversity by shrinking habitat, increasing edge and isolating populations [1].
• Isolated populations lose genetic diversity through inbreeding and cannot recolonise after local extinction [1].
• Rewilding reconnects fragments with corridors, restoring gene flow [1].
• Reintroducing missing species (e.g. large herbivores or predators) can restore food webs and natural processes [1].
• Allowing natural succession on abandoned land increases habitat diversity over time [1].
• Limitation: species already extinct cannot be restored; genetic diversity lost may not return [1].
• Limitation: recovery takes decades, the outcome is uncertain, and farmers or landowners may oppose land-use change and reintroduced predators [1].
• Limitation: invasive species or climate change may prevent the original community from returning [1].
• Conclusion: rewilding can reverse much of the loss where fragments can be reconnected and local people are involved, but it cannot restore everything lost [1]. [9] Examiner insight: “To what extent” needs a clear judgement tied to the evidence; the top of the range normally requires balanced arguments and a conclusion, not a list.

Where marks are usually lost

• Adding n instead of n(n − 1) in Simpson’s index, or forgetting that species with one individual contribute 0.
• Giving an index value without interpreting it in terms of richness and evenness.
• Using the final value, not the starting value, as the base for a percentage decline.
• Leaving units off a rate (individuals per year) or an area (km², ha).
• Subtracting the edge depth from only one side of a reserve.
• Skipping “gene flow stops” in speciation answers.
• Describing a data trend without quoting figures from the table.

Next steps

• Recap with the biodiversity and conservation revision notes.
• Re-learn weak areas in the biodiversity and conservation study guide.
• See the whole course on the IB DP ESS course hub.
• Tick off topics on the printable ESS syllabus checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026. The brief lists subtopics for Topic 1 only; the subtopic numbering on this page follows the printable ESS checklist.